1. Field of the Invention
The invention relates to a pair of glasses, a display system, and a control method thereof. More particularly, the invention relates to a pair of liquid crystal glasses, a projection display system, and a control method thereof.
2. Description of Related Art
With development of display technologies, besides features of lightness, slimness, shortness, and smallness, display devices are further developed to have a function of displaying three-dimensional (3D) images. Generally, a principle of displaying the 3D image is to respectively transmit two different images into a left eye and a right eye of a user, so that the user's brain may construct the 3D image.
Conventionally, a 3D projection display system is generally implemented by a projector and a pair of 3D glasses. Taking a digital light processing (DLP) projection technique as an example, a DLP projector is used together with a pair of 3D liquid crystal glasses.
Generally, each of the left and right lenses of the conventional 3D liquid crystal glasses uses a normally white liquid crystal shutter (LCS), wherein the normally white LCS is in a light transmitting state referred to as an ON state when a driving voltage is not applied, and the normally white LCS is in a light shielding stage referred to as an OFF state when the driving voltage is applied.
A time used for switching the ON/OFF states of the LCS is generally referred to as a response time. The response time includes a first switching time and a second switching time, wherein the first switching time is defined as a time required for switching the LCS from the ON state to the OFF state, and the second switching time is defined as a time required for switching the LCS from the OFF state to the ON state. Generally, twisted nematic (TN) or supero twisted nematic (STN) liquid crystal is used as the material of the LCS, so that the second switching time is greater than the first switching time.
To avoid a cross talk interference of the left and right eye images respectively transmitted by the DLP projector at different time, the switching time of the ON/OFF state all apply the second switching time, so as to avoid overlapping of the left and right eye images.
However, since the second switching time is greater than the first switching time, the above method may lead to an excessive long response time, a brightness reduction of the left and right eye images, an increasing of possibility of image flickering, and users' discomfort accordingly.
Moreover, FIGS. 1-4 of Taiwan Patent No. 548487 disclose a single-cell liquid crystal 3D shutter system including a linear polarizing film having a first polarization direction, a liquid crystal cell, an analyzer having the first polarization direction, and an analyzer having a second polarization direction, wherein the first polarization direction is perpendicular to the second polarization direction. Before an electric field is applied to the liquid crystal cell, the analyzer having the second polarization direction is pervious to light, and the analyzer having the first polarization direction is impervious to light. When the electric field is applied to the liquid crystal cell, the analyzer having the second polarization direction is impervious to light, and the analyzer having the first polarization direction is pervious to light. Moreover, FIG. 4 of the Taiwan Patent No. 548487 also discloses a design of switching the left and right glass lenses between a light transmitting state and a light shielding state.
Moreover, FIG. 3a and FIG. 3b of Taiwan Patent Publication No. 200836548 also disclose a projection display device including a controller, wherein the controller includes a synchronization signal generator, and the synchronization signal generator is, for example, a color wheel. To avoid the user sensing the synchronization signal, the synchronization signal may be displayed when the left and the right eye shutters are all closed. FIG. 4a of Taiwan Patent Publication No. 200836548 discloses shutter states of a pulse width modulation (PWM) sequence within a period of time, and traces thereof respectively represent a left eye shutter state and a right eye shutter state of an observing mechanism, wherein a time interval for switching the left eye shutter from the OFF state to the ON state is the same to a time interval for switching the right eye shutter from the ON state to the OFF state, and a time interval for switching the right eye shutter from the OFF state to the ON state is the same to a time interval for switching the left eye shutter from the ON state to the OFF state.